This invention relates to air-fuel mixture heating devices of the cylindrical shape using ceramic heaters, and more particularly it is concerned with an air-fuel mixture heating device for an internal combustion engine.
Ceramics formed of a composition comprising barium titanate as its principal constitutent by firing are known to have a low electric resistance at normal temperature and develop a very high electric resistance when a certain temperature near 120.degree. C. referred to as a Curie point is reached. Such ceramics are generally referred to as positive temperature coefficient (PTC) thermistors and have application as heaters. An air-fuel mixture heating device of the cylindrical shape is known which uses such ceramics. When such suction heating device is mounted immediately beneath a carburetor or a fuel injector, vaporization of fuel can be advantageously achieved. In this case, it is necessary to shield the ceramic heater from the atmosphere of gasoline as by a casing, in order to avoid the risk that the fragments of the ceramic heater might be drawn into the internal combustion engine when broken and to avoid the risk that the ceramic heater might undergo deterioration due to proximity to the atmosphere of gasoline. The casing is preferably formed of metal to completely isolate the ceramic heater from the atmosphere of gasoline and avoid its invasion by gasoline. Moreover, the casing should be provided with means for supplying oxygen to its interior to enable the heater having ceramics of barium titanate to function normally.